Script: By approximately 2 1/2 weeks, the epiblast has formed 3 specialized tissues, or germ layers, called ectoderm, endoderm, and mesoderm.
Ectoderm gives rise to numerous structures including the brain, spinal cord, nerves, skin, nails, and hair.
Endoderm produces the lining of the respiratory system and digestive tract, and generates portions of major organs such as the liver and pancreas.
Mesoderm forms the heart, kidneys, bones, cartilage, muscles, blood cells, and other structures.
|All ages referenced to fertilization, not last menstrual period.|